Electroluminescent source of light



OCt. 8, K JEGES ELECTROLUMINESCENT SOURCE OF LIGHT Filed Dec. 17, 1954 FIG1 FIG 2.

FIG 3 INVENTOR. KAROLY UEGES A TT'ORNEYS hood of the point of the needle.

ELECI'ROLUMINESCENT soURcE on LIGHT Karoly Jeges, Pecs, Hungary, assgnor to Egyesult Izzolampa Es Viliamossagi Reszvenytarsasag, Budapest, Hungary, 2 Hungarian enterprise Application December 17, 1954, Serial No. 475,986

Claims priority, application Hungary December 22, 1953 6 Claims. (Cl. 313-108) This invention relates to an electric source of light of the electroluminescent type of such kind as converts electrical energy in a direct manner into luminous energy.

It has been known from United States Patent No. 2,254,957, issued September 2, 1941, to make a source of light comprising a light permeable body of highly purified crystalline carbide capable of radiating light under the direct influence of current flowing therethrough and means for supplying current to said carbide, said current having a value materially below that necessary to produce incandescence. This phenomenon is one kind of electroluminescence and produces a so called cold light which latter arises owing to the effect of the current passing through the Carborundum (SiC) crystal, without substantially warming up the material.

This phenomenon showed a new path toward economical light sources of future. Since that time endeavors were made to obtain similar results using zinc sulphide, zinc oxide and Zinc silicate instead of Carborundum crystals. These materials, however, could be used for this purpose only when being excited by alternating current.

The object of the invention is to provide a source of light of the electroluminescent type by using a new material.

Another object of the invention is to provide a source of light of the electroluminescent type that may be sup plied with either direct or alternating current.

Other objects, features and advantages will appear from the following description and drawings, representing various embodiments of the invention.

According to the present invention similar electroluminescent eflects as described above can be produced by the use of crystalline stannic oxide (SnOz) having electrical conductance. It has been found that particularly such SnOz crystals having a crystal structure similar to that of natural cassiterite show useful electroluminescent efiects.

Experiments were made with the aforesaid stannic oxide crystal being interposed between a pair of electrodes. One of said electrodes was a metal needle, the point of which being in touch with the crystal body. The other electrode served as a holder of the crystal. The voltage was applied to the two electrodes. Under the influence of the current white light radiation was produced which phenomenon was observed in particular in the neighbour- As a result of observations carried out in a large scale it appeared that the intensity of light was mostly independent of the direction of the current. In some cases, however, a relation between light intensity and direction of current could be observed. In the latter case light radiation was more powerful with the current passing from the crystal toward the needle, that is to say, when the crystal was connected to the positive terminal of the current source. The voltage applied to the electrodes varied from to 300 volts, while the rate of current was ranging between microarnperes and milliamperes.

nited States Patent 0 Patented Oct. 8, 1957 Several natural crystals were also taken under investigation. It has been found that out of the investigated natural cassiterite crystals nearly all showed electroluminescent effect, in spite of the crystals being of different origin, thus containing impurities in different proportions, quality and quantity. These observations prove that the presence of impurities which make the crystal conductive play an important part in providing electroluminescent effect. Many of the natural impurities being present in cassiterite seem to be suitable to give rise to said phenomenon. The presence of traces of tin or oxygen being in excess to the stoechiometric formula SnOa of the crystal appear to be also suitable to produce the luminescent effect.

Three embodiments of the invention serving as examples are shown in the annexed diagrammatical drawing, in which:

Fig. 1 represents a source of light according to the invention comprising one crystal of SnOz interposed between two electrodes, in a side view,

Fig. 2 represents a second embodiment of the invention comprising a finely crushed powder of SnOz interposed between two electrodes having the shape of two plates,

Fig. 3 represents a third embodiment of the invention in its main features similar to the embodiment according to Fig. 2.

The source of light according to Fig. 1 consists of a crystalline body 5 of SnOz interposed between an electrode 6 forming a metal needle pressed with its point toward the crystal 1. The second electrode 7 serves as a holder for the crystal. 8 and 9 are the leads connected to the needle 6 and the holder electrode 7, respectively. The current, either alternating or direct is supplied to said electrodes by means of said leads.

Another embodiment of the invention which seems to be more practical is shown in Fig. 2, wherein 10a and 10b indicate two plates serving as the two electrodes which are fixed into a frame 12 of insulating material. 13 represents the finely crushed powder of SnOz crystalspreferably of the cassiterite type-being interposed between said two electrodes 10a and 10b, and 14a and 14b indicate the lead-ins to said plates. According to this embodiment of the invention one of the plates 10a and 10b be made of metal or any other conductive material, the other of a transparent and conductive material. Such transparent conductive materials suitable for this purpose are e. g. conducting glass or conductive plastic, such as known under the name Nesa. If desirable both plates may be made of the aforesaid transparent materials. Supplying alternating or direct current to the lead-ins, white light is produced due to the electro luminescence of the crystals.

A further embodiment of the invention is shown in Fig. 3, wherein similar numbers indicate similar parts as in Fig. 2. In Fig. 3 the plates 15a and 15b are made of a nonconductive material, e. g. glass or plastic, at least one of them being transparent. These plates are provided on their side contacting the crushed powder 13 of SnOz with a thin conductive layer or coating 11, which consists of a conductive material such as e. g. amorphus stannic oxide, cadmium oxide or the like. The coating provided on the transparent plate must also be transparent. Instead of applying a coating, a Wire-net may also be used as known in the art. Supplying alternating or direct current to the lead-ins connected to said coatings or wire-nets, respectively, white light is produced due to the electroluminescence of the crystal.

This invention is far from being exhausted by the examples enumerated above, because the particular nature of the source of light enables them to be constructed special purposes, without thereby deviating from the 7 direct influence of current flowing therethrough and means for supplying current to said body, said current having a value materially below that necessary to produce incandescence, said body consisting of crystalline stannic oxide having electrical conductance.

2. A source of light of the electroluminescent type comprising a body capable of radiating light under the direct influence of current flowing therethrough and means for supplying current to said body, said current having a value materially below that necessary to produce incandescence, said body consisting of crystalline stannic oxide having incorporated traces of impurities activating the crystal to luminescence.

3. A source of light of the electroluminescent type comprising a body capable of radiating light under the direct influence of current flowing therethrough and means for supplying current to said body, said current having a value materially below that necessary to produce incandescence, said body consisting of crystalline stannic oxide having electrical conductance owing to the traces of the impurities being present in said crystal.

4. A source of light of the electroluminescent type comprising a body capable of radiating light under the direct influence of current flowing therethrough and means for supplying current to said body, said current having a value materially below that necessary to produce incandescence, said body consisting of crystalline stannic oxide having electrical conductance and containing traces of an element selected from the group consisting of Sn and O, in excess to the stoichiometric formula.

5. A source of light of the electroluminescent type comprising a body in the form of a crystalline material capable of radiating light under the direct influence of current flowing therethrough, and means for supplying current to said material, said current having a value materially below that necessary to produce incandescence, said material consisting of a finely crushed powder of crystalline stannic oxide having electrical conductance,

said material being interposed between two conducting plates, at least one of said plates being transparent and said current being supplied to said plates.

6. A source of light of the electroluminescent type comprising a body in the form of a crystalline material capable of radiating light under the direct influence of current flowing'therethrough, and means for supplying current to said material, said current having a value materially below that necessary to produce incandescence, said material consisting of a finely crushed powder of crystalline stannic oxide having electrical conductance, said material being interposed between two plates, at least one of them being transparent, said plates being provided with a conductive coating on their side contacting the crystalline material and said current being supplied to said conductive coatings.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A SOURCE OF LIGHT OF THE ELECTROLUMINESCENT TYPE COMPRISING A BODY CAPABLE OF RADIATING LIGHT UNDER THE DIRECT INFLUENCE OF CURRENT FLOWING THERETHROUGH AND MEANS FOR SUPPLYING CURRENT TO SAID BODY, SAID CURRENT HAVING A VALUE MATERIALLY BELOW THAT NECESSARY TO PRODUCE INCANDESCENCE, SAID BODY CONSISTING OF CRYSTALLINE STANNIC OXIDE HAVING ELECTRICAL CONDUCTANCE. 